Evaluation of chemicals as inhibitors of trout cytochrome P450s.
This study examined the ability of several inhibitors of mammalian cytochrome P450s to affect hepatic P450-mediated monooxygenase activities in microsomes from beta-naphthoflavone (BNF)-treated rainbow trout. Three monooxygenase activities, namely, lauric acid (omega-1)-hydroxylase (LA-OH), 7,12-dimethylbenz[a]anthracene hydroxylase (DMBA-OH), and progesterone 6beta-hydroxylase (PROG-OH) activities were used as functional markers for trout hepatic CYP2K1, CYP1A1, and CYP3A27, respectively. The chemicals that were examined for their inhibitory effects were reversible, quasi-irreversible, or irreversible inhibitors of mammalian P450. At 100 microM concentration, the reversible inhibitors (ketoconazole, miconazole, and clotrimazole) were most potent in inhibiting LA-OH activity. These imidazole compounds, as well as ellipticine, parathion, and alpha-naphthoflavone, were the strongest inhibitors of DMBA-OH and PROG-OH activities. In addition, isosafrole, piperonyl butoxide, gestodene, 17alpha-ethynylestradiol, 1-aminobenzotriazole, and 5,8,11,14-eicosatetraynoic acid strongly inhibited PROG-OH activity. The global inhibitors, metyrapone, chloramphenicol, and allylisopropylacetamide, had very little or no inhibitory effect on trout LA-OH and DMBA-OH activities. Triacetyloleandomycin, a CYP3A inhibitor, did not affect PROG-OH activity catalyzed by trout CYP3A27. Diethyldithiocarbamate was an activator of LA-OH activity. None of the above enzyme activities was selectively inhibited by any of the chemicals when used at a concentration of 100 microM. There was no difference in the inhibition of LA-OH activities by representative P450 inhibitors between liver microsomes from untreated trout and BNF-treated trout. The results of this study suggest that inhibition data from mammalian studies could not be directly extrapolated to trout and likely other fish species and that care must be observed when mammalian P450 inhibitors are used to determine the participation of P450s in the metabolism and toxicity of xenobiotics in nonmammalian species.
Miranda
C L
CL
Department of Agricultural Chemistry, Oregon State University, Corvallis, Oregon 97331, USA.
Henderson
M C
MC
Buhler
D R
DR
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors; D042926:Cytochrome P-450 CYP4A; D065607:Cytochrome P-450 Enzyme Inhibitors; D000072467:Cytochrome P450 Family 2; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D029941:Fish Proteins; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors; D013329:Structure-Activity Relationship; D015262:Xenobiotics / Q000494:pharmacology*; D019324:beta-Naphthoflavone
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D029941:Fish Proteins; D007527:Isoenzymes; D015262:Xenobiotics; D019324:beta-Naphthoflavone; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; C037450:7,12-dimethylbenz(a)anthracene hydroxylase; D001189:Aryl Hydrocarbon Hydroxylases; C088323:CYP2K1 protein, Oncorhynchus mykiss; D019363:Cytochrome P-450 CYP1A1; D000072467:Cytochrome P450 Family 2; C022657:steroid hormone 6-beta-hydroxylase; D042926:Cytochrome P-450 CYP4A